ABSTRACT
we are in a class of the fourth grade. The teacher is dictating: ‘A circle is the position of the points in a plane which are at the same distance from an interior point called the center.’ The good pupil writes this phrase in his copy-book and the pupil draws faces, but neither of them understands. Then the teacher takes the chalk and draws a circle on the board. ‘Ah’, think the pupils, ‘why did’t he say at once, a circle is a round, and we should have understood.’
